The story of an explicit relationship between a man and his sister-in-law.

CEO Seung-tae is in an affair with his sister-in-law So-young who works for him. One day, a rookie named Young-chul finds out about them and threatenens So-young that he'll tell the CEO's wife about them and spends anight with her. He continues to threaten and bully her. So-young is scared that her affair with her brother-in-law will cause trouble with her half-sister Hye-sun...

Yoo-jin and Myeong-seok get a call from Hye-jin in the middle of the night. She finally escapes from domestic violence and comes to live with her sister. However, Myeong-seok is nice to her and Hye-jin starts to feel fond of him...

Yong-hoon, who is currently separated with his wife, Bo-mi, consults her sister-in-law Bo-young how to change her sister's mind. Due to their frequent meeting, Yong-hoon is drawn to his sister-in-law, Bo-young and crosses the line that shouldn't be crossed.